Sexual desire traced to genetics

Scientists in Israel have pinpointed a common genetic trait that could make some of us hungrier for sex than others.

The team looked at a gene known as the dopamine D4 receptor (DRD4), which partly controls the brain's response to dopamine, a chemical often associated with the body's 'pleasure system'. Scientists know that this neurotransmitter can control sexual behaviour in animals and humans, and that dopamine circuits help to create the drive for things such as sex, drugs and food.

Richard Ebstein at the Hebrew University in Jerusalem was prompted to examine the DRD4 gene after a 2004 study showed that a drug blocking this gene's function helped to trigger erections in rats1.

Ebstein and his colleagues asked 148 male and female college students to fill in a sex questionnaire that posed questions such as 'How important is sex in your life?' and 'How often do you have sexual fantasies?'

They used the answers to tot up scores showing how much each student desired sex, how much they were aroused by sex and how good they were at performing the deed: effectively a measure of their 'horniness', Ebstein says. Then the team matched up these scores with the genetic make-up of each student's DRD4 gene.

The researchers found that students with one particular version of the gene scored roughly 5% lower, on average, in sexual desire than those with an alternative gene variant; a small but statistically meaningful difference. Around 70% of the population carry the low-arousal version and some 20% carry the high-arousal version of the gene. Their findings appear online in the journal of Molecular Psychiatry2.

Pleasure seekers

The researchers don't know exactly how this genetic change may boost libido, because dopamine has many functions in our brain that influence our behaviour.

There is some evidence that the DRD4 gene is linked to novelty-seeking, so the people who crave more sex might simply be the type that craves more excitement generally. Also, dopamine may influence how sharply the brain reacts to sexually arousing stimuli and prompts bodily reactions such as an erection.

The finding fits with other studies showing, for example, that patients who take dopamine-boosting drugs used to treat Parkinson's disease also experience a jump in sex drive. But other experts say that the finding has to be repeated in a much larger group of people before it can be confirmed.

Taboo

An array of different genes probably moulds our sexual desire and behaviour, along with cultural expectations, upbringing and life experiences. But taboos around sex make the genetic underpinnings hard to research, says Dean Hamer of the National Institutes of Health in Bethesda, Maryland, who authored a controversial study linking genetic variation to homosexuality3. "There's a cultural ban on sexuality studies," he says.

Hamer argues that such research is important because sex is a fundamental part of human behaviour and could, for example, explain why some people seek multiple sexual partners, which contributes to the spread of sexually transmitted diseases. Ebstein adds that people who aren't that excited by sex may find it reassuring to know that this may be partly down to their genes.

"The most important thing is it forwards scientific study of sexuality," Hamer says. "It's about time people started studying this stuff."